Step 7: Grout the joints

Grout the joints
Photo: Kolin Smith
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Using a grout sponge and/or a putty knife, clean out any joints where the thinset has squeezed out. Once the tiles are set, clean, and evenly spaced, leave the thinset to dry for 24 hours. Remove the spacers.

Following the directions on the packaging, mix the grout with water until it resembles peanut butter. Using a grout float held at at angle, spread a layer of grout diagonally across the joints, pushing the mix between the tiles. Work the float in all directions to ensure all the joints are full; never sweep it parallel to the joints or it will catch in the gaps and pull up the mix. Do not grout the joint around the edge of the hearth.

Once the joints are well packed, turn the float on edge and, again sweeping diagonally across the joints, scrape off the excess grout. Let the grout dry about 30 to 60 minutes, until firm to the touch.

Dampen a grout sponge and squeeze out the excess water. Wipe the surface of the tiles in a circular motion to clean off the excess grout. Once the tiles look fairly clean, leave the grout to dry overnight, until a thin haze covers the tiles. Then, using a clean, dry rag, buff off the haze.

Fill the joint around the perimeter of the hearth with caulk that matches the grout. Smooth the caulk with a wet finger. Allow the hearth to set for another two or three days before building a fire.
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    Tools List

    • utility knife
      Utility Knife
    • drill
      Drill/Driver with mixing paddle
    • notched trowel
      3/8-Inch Notched Trowel
    • caulk gun
      Caulking Gun
    • wet saw
      Wet-cutting Tile Saw
      (rents for about $40 a day)
    • four-foot level
      4 Foot level
    • putty knife
      Putty Knife
    • rubber float
      Rubber Grout Float
    • grout sponge
      Grout Sponge

    Shopping List

    1. TILES
    Available at home centers and tile dealers, though most high-end tile requires ordering as much as six weeks in advance. Tiles are sold by the square foot, ranging in price from $2 to about $50. You should look for tiles with a foot-traffic rating of 3 or above (on a scale of 1 to 5). Given a set of measurements, some tile dealers will calculate how much you need, and art-tile manufacturers may make you all the tiles, in the right sizes, to order. But you can also determine the square footage yourself: Multiply the length in inches by the width, and divide the result by 144. Then add 10 percent to that number for waste cuts.

    2. ½-INCH CEMENT OR FIBER-CEMENT BACKER BOARD
    to go over a plywood subfloor and create a flat, stable surface for installation.

    3. CONSTRUCTION ADHESIVE
    to glue backer board to the subfloor.

    4. 11/4-INCH BACKER-BOARD SCREWS
    to screw the backer board to the subfloor. 5. UNMIXED THINSET MORTAR
    Also known as setting cement. One 50-pound bag should be enough. Do not use mastic; it can’t take high heat.

    6. LATEX ADDITIVE
    to mix with the thinset, as the liquid. It improves flexibility and creates a stronger bond than a water-based mix.

    7. TILE SPACERS
    Porcelain tiles can have as little as a 1/8-inch gap between them, while ceramic tiles can be 3/6 to 3/8 inch apart and terra-cotta tiles can be spaced 3/4 inch apart. Handmade tiles may require special surface spacers that accommodate irregularities on the top edge. Buy spacers appropriate for your tile type and the grout lines your layout dictates.

    8. GROUT
    Use sanded grout if the space between your tiles will be greater than 1/8 inch, unsanded if it’s smaller. You can also buy colored grout to more closely match your tile.